Hawaii’s Department of Land and Natural Resources (DLNR) has authorised the inspection of dams and reservoirs in the county of Kauai following the collapse of Kaloko dam last week.
In an emergency meeting held on 16 March, DLNR authorised the Department of the Attorney General and its agents, employees, consultants and investigators to enter private property for the purposes of investigating and inspecting dams and reservoirs located within Kauai county pursuant to Hawaii Revised Statutes Chapter 179D.
There are 133 dams in DLNR’s Hawaii Inventory of Dams. Fifty-three of these dams are in Kauai, with 13 state owned and 40 privately owned. Under the Federal Emergency Management Agency’s Hazard Potential Classification System for Dams, 23 of these dams have been classified high hazard, eight are significant with the remainder low or undetermined hazards.
DLNR is now instructing all dam or reservoir owners to immediately inspect and report back to the department the nature and condition of their structures. In addition, all recent maintenance records and documentation of operations and inspections are being requested. DLNR is also instructing owners to evaluate, and update if necessary, their emergency preparedness plans, including evaluation of potential downstream impacts should the dam or reservoir breach or partially breach.
Currently four DLNR engineers are in Kauai to inspect reservoirs and dams. The DLNR Dam Safety Section head is consulting with Kauai County Public Works Engineers on addressing Kaloko reservoir.
Kaloko breached on 14 March, releasing an estimated 1.7Mm3 of water. Three bodies have so far been recovered from the floodwaters, with up to seven others missing.
DLNR, the Hawaii State Civil Defense and the USGS Pacific Islands Water Science Center are now carrying out a hydrologic and hydraulic assessment of the dam break. This assessment will: document the distribution of rainfall in the area prior to and during the event; document the runoff conditions in the area prior to and during the event; document maximum water levels in Kaloko reservoir prior to failure and in the Morita reservoir subsequent to the failure; document the status of inflow and outflow to the reservoir prior to the failure (inflow appears to be partly via the Kaloko ditch); compute the volume of water that was released from the Kaloko reservoir as a result of the failure; compute peak discharge rates in Wailapa Stream between the Kaloko and Morita reservoirs and in Wailapa Stream downstream from Morita; document maximum water levels and areas of inundation associated with the flooding along Wailapa Stream; and determine amounts of scour and deposition of sediment along Wailapa Stream channel between Kaloko reservoir and the ocean.
USGS headquarters has provided some funding from the national flood reserve to offset some costs of a hydrologic/hydraulic assessment and the local USGS office has some federal matching funds available. The state is expected to reimburse some of the USGS costs.